The present invention is directed to apparatus for converting a dc or analog signal to a digital signal with minimum drift and more specifically, where the analog signal is produced by a resistance temperature detector element.
In the processing of, for example, food or drugs it is desirable to record processing temperature to insure that adequately high temperatures have been used. A typical temperature sensor is a resistance temperature detector (RTD). This produces a dc or analog signal which must be amplified and processed. Amplification of dc signals, of course, has the inherent problem of dc drift. This problem has been met by chopper stabilization or by use of a storage capacitor to provide an indication of drift and attendant correction. Both of the foregoing solutions do not work successfully under high ambient temperatures or require trimming of circuit components to minimize drift error. Other types of processing circuits are of an excessively large size with poor accuracy.